Hi @VACRMH, you can create custom filters in LaunchBox via the side bar. You'd select Custom Filters from the dropdown at the top, and then click the + button on the sidebar to add a new one. Then of course just put Arcade in the Platform field and Fighting in the Genre Field, give it a name, and save it. That should give you a custom filter that displays all the Arcade Fighting games.
Then in Big Box, just back out from the default platforms screen and select View Custom Filters, which will show you Arcade Fighting as an option. Obviously it's not hierarchical like you're ultimately looking for but it's a start at least. :)